A/C clutch stays engaged

Good afternoon.

I attached a diagram for you of the A/C controls.

From the looks of it, the climate control head is commanding the compressor on all the time. It sends a signal to the ECM to turn on and when you turn off the A/C, the signal is still being sent.

That is why it disconnects when you remove the wires from the low pressure switch.

From all indication you may have a bad control head.

Roy

I will get one tomorrow and let you know the results.

Keep us updated.

Roy

Roy, before I get a command center let me say that the compressor clutch would stay engaged all the time. Even when the pressure should have made it turn off. I have replaced; compressor, dryer, expansion valve.

Okay, do you mean if you have less than 20 lbs of pressure on the low side, the compressor is still engaged?

Roy

Yes sir, clutch stays on. Pressure is not cycling 35 low 150 and up on high.
Could this be a problem with the control center?

At 35, the clutch will stay engaged. It has to drop below 20 to disengage the clutch.

Roy

Okay, Let me start over, I have had my vehicle to shops. Not a whole lot was resolved. It appears I have a ground problem, that was the answer from the A/C shop. The electrical auto guy says it is a thermostatic meter. Let me just reiterate, I did find a wire crossed at pressure switch to make the compressor run 100% of the time (fixed) The compressor, pressure switch, expansion valve, dryer have all been replaced, system has been evacuated, flushed, but the pressure is running to high on the high side. The cycling time is not right.
My understanding is the signaling for it to go from high to low cycling is not right. Can someone tell me a common reason for this? might add the relay has been checked and it shows that if you ground it the compressor kicks on when its not on. Maybe this is a clue.
Signed, in over his head.

Okay.

Lets start with the pressures.

Can you give me the high and low side pressures while the engine is running and I need the outside temperature as well?

Roy

Eighty degrees outside (Texas). Low 35 are so, high going up to 250.

Okay, spray some water on the condenser and see what happens.

The high side is too high.

It should be around 175 with the ambient temperature.

Roy

Okay, So I took my vehicle to a couple of hack shops, The A/C shop told me I had a ground problem so he sent me to a auto electric shop. The guy at the electric shop tried to convince me to run a ground from the relay so the compressor would stay on (all the time), not knowing I knew better.
So he diverted to it is the thermostic reader on the EVAP. Nope I replaced that. Needless to say he charged $40.00 for what I already knew. A/C blows cold air but will not cycle properly. Help!

I suggested some testing in my last response.

Any results? It will help me help you if you can give the information that I suggested.

Roy

I have this exact issue haunting me right now. If you can name it, I have changed it. Compressor, condenser, evaporator, expansion valve, dryer, triple pressure switch, relays, thermal control amp, control head and even swapped the ECU! Something on my car is telling something the A/C should be running. I even get both fans running too! I have spent hours and hours pouring over wiring diagrams trying to find out where this thing is getting a ground to close the AC relay. I have shot all wires in this system to the ECU and I have nothing grounding out. I have a work around in mind. It is a thirty degree old school mechanical switch stuffed onto the EVAP core, a relay and a master kill switch for winter use. GLYN, if you get any further along, please post it here. My air is nice and cold, has the right amount of PAG and refrigerant, but when the car starts, I can hear the clutch engaging with the system turned off. Very weird!

That is a good one, I have the wiring diagrams here and I am looking over as well, you can confirm that when you remove the ground (pink wire) from the ECU the compressor turns off? Pink wire grounding th relay. Please confirm this so we can continue.

Here are the wiring diagrams so we can be on the same page.

Please report back

Cheers, Ken

That is the first good idea I have heard yet! I will remove that signal wire from the ECU from the relay tomorrow and report back my findings. If this shuts off the compressor, then we at least know which direction to look. Thank you.

Yes, trial and error we will find the problem.

Ken, I removed the signal wire running from the relay back to the ECU. Compressor clutch disengaged and both rad fans stopped running. I was talking with the guy at O'reillys. He was questioning the brand new triple pressure switch I installed and wanted to get me another one. Sure, he is not the one that has to reclaim, vacuum and recharge 134a. :-/
Back into the wiring diagrams I go.

Can you test the AC switch to make sure the signal is being cut when the switch is off? If the switch is stuck on this will cause the problem.

I will do you one better Ken. I swapped out the complete control head with another today and same deal. I am really starting to give the new pressure switch the stink eye. I have a spare stock Nissan one and I am going to try that next. Seems to me right after I rebuilt the entire AC system, I had rapid clutch cycling. So it was then I bought a new pressure switch and that was when I discovered I could never shut the silly thing off. O'Reillys said I probably got a faulty switch from them. Needless to say, I am not going to try another new one. Who knows, maybe the new ones are not wired correctly? And I have no desire to figure it out either. lol

Ken, I installed a used Nissan pressure switch tonight, vacuumed and recharged and finally when I shut the AC switch off it actually turns off. I will be taking my brand new pressure switch back to O'Reillys and they better have some money waiting for me. Their faulty new switch has cost me a butt-load of time, refrigerant, parts chasing, a control panel and on and on and on. Thanks for making me stay in the fight until I sorted this out. I was ready to go old school, but what bothered me was the IACV was activated all the time due to the ECU getting the signal for AC. I bet vital parts of my anatomy the new switch is wired wrong. Good lesson for anyone reading this in the future is never completely rule out brand new parts and always return to the scene of the crime. I like to say look at the last thing you messed with. Best wishes man and thanks again!

Yep , "old school" my favorite. Glad you hung in there to feel right when you finish the repair. Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken

I bought this truck not to long ago and noticed the air conditioner did not work. So I checked the high pressure and it was extremely too high so I let the pressure out to where it should be. After that I noticed the clutch still did not engage, so I direct wired the compressor to the battery and the clutch engaged. I proceeded to buy a new air conditioner relay and the clutch still did not engage?

So with the air conditioner compressor not working the pressure on the high side read too high? what did it read before you started letting charge out of the system?

It was between 120-150 psi.

I have seen 120 psi without the compressor running. That is just the pressure of the gas. So has the air conditioner ever worked since you have owned it? If so was this the first time it stopped blowing cold?

No, it has never worked. I have only owned the truck for a week.

Okay, so what is the pressure now? One problem is we do not know if the system is fully charged under charged or over charged. Have you checked the high/pressure switch?

How do you test it? I have taken the connector off and put my test light in it and it does not light up, but it changes the rpm's?

Also the pressure last night was 35 psi.

Also, when I turn the truck on and i put it on max air conditioner it changes the rpm's, but the clutch is not engaged.

35 psi is low for static pressure. sometimes the computer will kick up the rpm's when the air conditioner is turned on. The pressure switch simply connects the two wires together to it when the correct pressure is pushed against it. You can use a ohms meter to see if it is connecting to let the air conditioner compressor come on.

I will try that in the morning. What psi should I be at? air conditioner's are not my specalty. lol

I will see what I can find out Ia m not exactly sure, but most I have seen are 80 psi plus. Also, try this start it up turn on the air conditioner and jump the terminals of the pressure sensor connector and see if the air conditioner compressor turns on only jump it for a few seconds.

23-33 psi between terminals one and three there should be continuity on the high /low switch itself.

So, I put my volt meter on it and it is getting power, when I re-hooked the connector back up to the pressure switch the rpm's went up then back down.

You are not looking for voltage your looking for continuity across pins one and three on the pressure switch itself.

How do I test continuity?

Sorry stupid auto correct how do I test continuity?

https://www.2carpros.com/articles/how-to-use-a-voltmeter



I posted the link to how to check continuity.